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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Produce Safety and Microbiology Research » Research » Publications at this Location » Publication #147386

Title: GENETIC DIVERSITY OF XANTHOMONAS CAMPESTRIS PV. VITIANS, THE CAUSAL AGENT OF BACTERIA LEAFSPOT OF LETTUCE

Author
item Barak Cunningham, Jeri
item GILBERTSON, ROBERT

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2003
Publication Date: 5/20/2003
Citation: BARAK CUNNINGHAM, J.D., GILBERTSON, R.L. GENETIC DIVERSITY OF XANTHOMONAS CAMPESTRIS PV. VITIANS, THE CAUSAL AGENT OF BACTERIA LEAFSPOT OF LETTUCE. PHYTOPATHOLOGY. 2003. 93:596-603

Interpretive Summary: Bacterial leafspot of lettuce (BLS) has become more prevalent in many lettuce-growing areas of the world over the past decade. To gain insight into the nature of these outbreaks, the genetic variation in strains from different geographical locations was examined. All strains were first tested for pathogenicity on lettuce plants, and then genetic diversity was assessed. Fatty acid analysis identified all pathogenic strains as the same species, however this method did not consistently identify all the strains as the same pathogen. DNA fingerprints and sequence analysis of all lettuce pathogenic strains examined were identical, and distinct from those of the other related plant pathogens. Thus, these characteristics did not reveal genetic diversity among the causal agent of BLS, but did allow for differentiation of it from other closely realted plant pathogens. Genetic diversity among the strains was revealed by analysis with a repetitive DNA probe and by characterization of plasmid DNA. This diversity was greatest among strains from different geographical regions, although diversity among strains from the same location also was detected. The results of this study suggest that the strains which cause BLS are not clonal, but comprise a relatively homogeneous group.

Technical Abstract: Bacterial leafspot of lettuce (BLS), caused by Xanthomonas campestris pv. vitians, has become more prevalent in many lettuce-growing areas of the world over the past decade. To gain insight into the nature of these outbreaks, the genetic variation in X. campestris pv. vitians strains from different geographical locations was examined. All strains were first tested for pathogenicity on lettuce plants, and then genetic diversity was assessed using (i) gas-chromatographic analysis of bacterial fatty acids, (ii) PCR analysis of repetitive DNA sequences (rep-PCR), (iii) DNA sequence analysis of the internal transcribed spacer region 1 (ITS1) of the ribosomal RNA, (iv) RFLP analysis of total genomic DNA with a repetitive DNA probe, and (v) detection and partial characterization of plasmid DNA. Fatty acid analysis identified all pathogenic strains as X. campestris, but did not consistently identify all the strains as X. campestris pv. vitians. The rep-PCR fingerprints and ITS1 sequences of all pathogenic X. campestris pv. vitians strains examined were identical, and distinct from those of the other X. campestris pathovars. Thus, these characteristics did not reveal genetic diversity among X. campestris pv. vitians strains, but did allow for differentiation of X. campestris pathovars. Genetic diversity among X. campestris pv. vitians strains was revealed by RFLP analysis with a repetitive DNA probe and by characterization of plasmid DNA. This diversity was greatest among strains from different geographical regions, although diversity among strains from the same location also was detected. The results of this study suggest that these X. campestris pv. vitians strains are not clonal, but comprise a relatively homogeneous group.